The present invention relates to water-base ink, a method of manufacturing the ink and a printing method using the ink, and in particular, to ink that is ideal for inkjet printing on a print surface where water-base solvent does not permeate, such as on a printed substrate.
Ink jet printing is a printing method in which small drops of ink are ejected out of a nozzle to attach to a printing surface of a print medium, such as paper or other medium, and then solvent is dried from the attached ink (the attached ink from which the solvent is dried is hereafter referred to as the ink attachment) and the colorant is fixed on the printed surface. This method enables high-speed printing of high-resolution and high quality images. In general, ink used in ink jet printing has a water-base solvent as the main component, to which colorant and a penetrant such as glycerin (additives used to prevent clotting) are added.
However, if the printing surface is made of a surface which makes the permeation of a water-base solvent extremely difficult or even impossible, for example, board or film surfaces made of regular paper, cloth, metal, phenol, melamine, vinyl chloride, acrylic or plastic such as polycarbonate, execution of ink jet printing using the aforementioned ink designed for normal ink jet printing becomes difficult.
For this reason, in this type of usage, it becomes necessary to have the ink contain an ingredient which enables stable fixing of colorant (an ingredient which remains as a film on the printing surface after being dried).
Moreover, when printing is performed on printed substrates and the like, the ink must dry quickly, and the ink film must have a high level of chemical proof properties, and the ink film must be very hard.
As an example of ink with the aforementioned qualities, Japanese Laid Open Patent Publication 3-216379 discloses an ink jet ink that contains a colorant and an ingredient which becomes polymerized upon radiation of ultra-violet rays (polymerizing monomer, oligomer, or photoinitiator).
Moreover, U.S. Pat. No. 5,623,001 discloses ink jet ink that contains water, and polymerization material (oligomer or mixture of oligomer and monomer) which admixes with water and hardens with ultra-violet rays, photoinitiator and colorant.
Furthermore, Japan Laid Open Patent Publication 3-220218 discloses a screen printing ink component that hardens with ultra-violet rays and which contains polyurethane (meth) acrylate resin, N-vinyl pyrrolidone, acryloyl morpholine, photoinitiator and pigment.
In the ink described in these publications, photoinitiators in the ink attachment are activated by irradiation of ultra-violet rays after the ink is attached on the printing surface, and a polymerizing oligomer and/or a monomer""s polymerizing reaction is generated, which polymerization fixes colorant in the ink attachment on the printing surface. Hence, it is expected that the ink attachment will dry in a short time and a hard ink film with a high level of chemical proofness will be obtained with a high color concentration and uniform printing without smearing and unevenness.
However, the ink described in these publications needs to be enhanced in terms of stability and ink film strength.
An object of the present invention is to provide a photo polymerization type water-base ink having an extremely high level of printing stability and ink film strength after light irradiation when used in ink jet printing, such as providing ink with an enhanced capability for ink jet printing onto a printed substrate.
In order to achieve the aforementioned object, the present invention provides photo polymerization water-base ink including colorant, photo polymerization resin, photoinitiator, and water-base solvent. The photo polymerization resin includes oligomer particles in the emulsion state and a monomer residing in the oligomer particles. The polar solvent includes one or more of 2-pyrrolidone, N-acryloyl morpholine and N-vinyl-2-pyrrolidone with weight ratio of between 0.1 to 10 is also contained.
In this ink, because photo polymerizing ink includes oligomer particles in the emulsion state and monomer residing in the oligomer particles, the photo polymerization resin is dispersed uniformly in the ink and is maintained in this condition for a long time. Moreover, because the polar solvent includes one or more of 2-pyrrolidone, N-acryloyl morpholine and N-vinyl-2-pyrrolidone with a weight ratio of between 0.1% to 10%, an extremely high level of printing stability is obtained when used in ink jet printing.
In the water-base ink of the present invention, the polar solvent preferably contains 2-pyrrolidone and N-acryloyl morpholine.
By so doing, water-base ink of the present invention assures an extremely high level of printing stability and ink film strength after light irradiation when used in ink jet printing.
Moreover, the present invention provides photo polymerization water-base ink, including: colorant, photo polymerization resin, photoinitiator, and water-base solvent that includes polar solvent having a reactive group (vinyl radical, acryl radical, metacryl radical and others) reacting with photo polymerization resin.
The ratio of the polar solvent in the ink, for example, a weight ratio of between 0.1% to 10%, preferably between 1% to 7%.
This ink exhibits a high level of storage stability with an extremely high level of printing stability, strong ink film and superior chemical proof property when used in ink jet printing. As indicated in 1 and 2 below, these advantages may be provided due to a polar solvent containing a reaction radical which reacts with photo polymerization resin.
1. Because polarity of the solvent is large compared to that of a normal surfactant used to secure printing stability, the dissolution power of the solvent with respect to water is large. Therefore, the solvent does not distort the dispersion properties between the colorant and the photo polymerization resin and enables stable dissolution or dispersion of the ingredients which make up the other ink components. This solvent, because it has a polymerizing reaction radical in its molecular structure, achieves high bridge density in the film.
2. N-acryloyl morpholine and N-vinyl-2-pyrrolidone are typical examples of the solvent.
In the water-base ink, the photo polymerization resin preferably includes oligomer particles in an emulsion state and monomers residing in the oligomer particles.
Polyesteracrylate, polyurethaneacrylate, epoxyacrylate, polyetheracrylate, oligoacrylate, alkidacrylate and polyoleacrylate are some of the examples that can be used as oligomer in the present invention. Of these, it is preferable to use polyesteracrylate or polyurethaneacrylate.
In the present invention, molecular weight of the oligomer to be used is in the 500-20,000 range, preferably in the 500-10,000 range.
In the ink of the present invention, the oligomer content in terms of the percentage weight is in the 1% to 50% range, and preferably in the 3%-30% range.
Monofunctional acrylate and methacrylate, multifunctional acrylate and metaacrylate are examples of monomers that can be used in the present invention. These monomers having low molecular polyole acrylate and methacrylate have the merit of low viscosity and speedy hardening properties. The following are typical monomers which may be used in the present invention: diethyleneglycol diacrylate, neopentylglycol diacrylate, 1,6 hexanedioldiacrylate, hydroxypropyl ester-neopentyl-glycoldiacrylate, trimethylol-propane-triacrylate, pentaerythritol-triacrylate, dipenthacrythritol-hexaacrylate, acryloyl-morpholine, 2-phenoxy-ethylacrylate, phthalic acid-hydrogen-(2,2,2-triacrylonitrille-oxymethyl)ethyl, dipentaetythritol-polyacrate, dipentaerythritol-polyacryrate, and others.
Of these listed above, acryloyl morpholine, 2-phenoxyethylacrylate, phthalic acid hydroen-(2,2,2,-triacrylonitrille oxymethyl0ethyl, dipenthaerythritol-polyacrylate, dipentaerithrytol-polyacrylate are preferred monomers.
In the present invention, the molecular weight of the monomer to be used is in the 100-3,000 range, and preferably in the 100-2,000 range.
In the ink of the present invention, the monomer content in terms of the percentage weight is in the 1% to 70% range, and preferably in the 3%-50% range.
Here, because the oligomer and the monomer are copolymerized to form a 3-dimensional substance, the ratio of oligomer and the monomer in the ink should be determined considering polymerization efficiency, polymerization speed, post-polymerization contraction rate, and the film strength of the polymer and the like. In fact, the ratio of the oligomer and the monomer in the ink should be in the range of 95 to 5 (oligomer to monomer)-40 to 60, and preferably the range of 90 to 10-50 to 50.
Typical photoinitiators to be used in the ink of the present invention are those which start the polymerization of the photo polymerization resin (oligomer and monomer) by absorbing ultra-violet rays in about the 250 nm-450 nm range, for example, and generating radicals or ions. Typical photoinitiators which may be used in the ink of the present invention are as follows:
benzoinmethylether, benzoinethylether, isopropylbenzoinether, isobutylbenzoinether, 1-phenyl-1,2-propanedione-2-(0-ethoxycarbonyl)oxime, benzyl, diethoxyacetophenone, benzophenone, chlorothioxanthone, 2-chlorothioxanthone, isopropylthioxanthone, 2-methylthioxanthone, isopropylthioxanthone, 2-methylthioxanthone, polychlorinatepolyphenyl, hexachlorobenzen and others.
Of these, isobutylbenzoinether, 1-phenyl-1,2-propanedione-2(0-ethoxycarbonyl)oxime are preferred.
Photoinitiators which are usable in the ink of the present invention are sold under the following product names and are easily obtainable. Vicure 10, 30 (made by Stauffer Chemical), Irgacure 184, 651, 2959, 907, 369, 1700, 1800, 1850, 819 (made by Chiba Specialty Chemicals), Darocurel 173 (made by EM Chemical), Quantacure CTX, ITX (made by Aceto Chemical), Lucirin TPO (made by BASF).
Either pigment or dye, as long as it disperses in the water, may be used as a colorant in the ink of the present invention. However, in the case of printing on a printed substrate, the use of a pigment is preferred.
Either an inorganic or organic pigment may be used as a pigment. Titanoxide, iron oxide and carbon black are examples of an inorganic pigment that can be used. Any carbon black which is produced using publicly known methods such as the contact method, the furnace method or the thermal method may be used.
Azo pigment (including azolac, insoluble azo pigment, concentrated azo pigment, chelate azo pigment), polycyclic pigment (for example, phtalocyanin pigment, perylene pigment, anthraquinone pigment, quinacridon pigment, dioxzine pigment, thioindigo pigment, iso-indolinone pigment, quinofuraron pigment), dye chelate (for example, alkaline dye chelate, acid dye chelate), nitro pigment, nitroso pigment, and aniline black are examples of organic pigment that can be used.
In the ink of the present invention, colorant is preferably added as a colorant dispersion liquid to be obtained by being dispersed in the water-base solvent with dispersion agents or surfactant. The use of a dispersion agent which is commonly used to prepare a colorant dispersion liquid, such as a high polymer dispersion agent, is preferred. Here, the dispersion agent and surfactant to be contained in the colorant dispersion liquid naturally function as the dispersion agent and surfactant of the ink ingredient other than the colorant.
In the ink of the present invention, the colorant content in terms of the percentage weight is in the 1% to 50% range, and preferably in the 2%-30% range.
The ink of the present invention contains, as water-base solvent, water or a mixture of water and water-base organic solvent having a low boiling point. Pure water or super-pure water such as ion exchange water, ultra filtration water, reverse osmosis water or distilled water may be used. Moreover, use of water sterilized by the irradiation provided by ultra-violet rays or the addition of hydrogen peroxide is desired for the prevention of mold and bacteria generation when the ink is stored for a long time.
Methanol, ethanol, N-propylalcohol, iso-propylalcohol, n-butanol, sec-byutanol, tert-butanol, iso-butanol, n-pentanol are examples of water-base organic solvent having a low boiling point. Of these, the use of univalent alcohol is preferred. Use of these solvents enables a reduction in ink drying time.
When organic solvent with low boiling point is added as a water-base solvent to the ink of the present invention, the amount to be added is preferably between 0.1% to 10% in terms of the percentage weight, and more preferably between 0.5% to 5% in terms of the percentage weight.
The water-base ink of the present invention preferably contains penetrant which includes an organic solvent having a high boiling point other than the polar solvent.
The following are examples of organic solvent having a high boiling point to be added as a penetrant to the ink of the present invention, multi-valiant alcohol such as ethyleneglycol, diethyleneglycol, triethyleneglycol, polyethyleneglycol, polypropyleneglycol, propyleneglycol, butyleneglycol, 1,2,6-hexantriole, thioglycol, hexyleneglycol, glycerin, trimethyrolethan, trimethyrolepropane; multi-valiant alkylether such as ethyleneglycolmonoethylether, ethyleneglycolmonobutylether, diethyleneglycolmonomethylether, diethyleneglycolmonoethylether, diethyleneglycolmonobutylether, triethyleneglycolmonomethylether, triethyleneglycolmonoethylether, triethyleneglycolmonobutylether; urea, 2-pyrolidone, N-methyl-2-pyrolidone, 1,3-dimethyl-2-imidazolidinone.
In the ink of the present invention, the content of penetrant in terms of a percentage weight should be between 5% to 40%, and preferably between 2% to 20%.
The ink of the present invention may contain multi-valiant metallic salt, polyarilamin or its derivatives, inorganic oxide colloid, penetrant, pH adjuster, an anti-corrosion agent and/or an anti-mold agent.
As the oligomer, the water-base ink of the present invention preferably contains a urethane oligomer in the range in terms of a percentage weight of between 3% to 10%. As the monomer, the water-base ink of the present invention preferably contains dipentaerythritol polyacylate in the range of between 3% to 10%, in terms of percentage weight. The ink also preferably contains 2-pyrrolidone and N-acryloyl morpholine in a combined range of 0.1% to 10% in terms of percentage weight, a photoinitiator in the range of 0.3% to 2.0% in terms of percentage weight, ethylene glycol in the range of 2% to 20% in terms of percentage weight, and pigment including titanium dioxide particles, as colorant, in the range of 3% to 20% in terms of percentage weight.
Moreover, the present invention provides an ink production method, of a type of water-base ink, wherein monomer is added to and agitated in an emulsion where oligomer is dispersed in the water, resulting in monomer residing in the oligomer particles in emulsion state, after which the process ingredients other than the photo polymerization resin are added to the liquid obtained through the process.
In this method, the photoinitiator may be added to an emulsion with the monomer during the process, or it may be added to the liquid obtained through the process.
Moreover, the present invention provides an ink jet printing method wherein the ink is attached on the printing surface in a predetermined shape by ejecting water-base ink with an ink jet apparatus, after which colorant is fixed on the printing surface by polymerizing photopolymerization resin in the attached ink by irradiating light on the printing surface.
In this method, use of ink containing a photoinitiator which is activated by ultra-violet ray irradiation is preferred, with ultra-violet ray irradiation conducted as the light irradiation.
In this case, ultra-violet ray irradiation is preferably conducted with an ultraviolet illumination of 100-10,000 mJ/cm2.
These steps assure a sufficient polymerization reaction and deterioration of colorant by ultra-violet ray irradiation is prevented. More preferable ultra-violet irradiation is 500-5000 mJ/cm2.
Metal halide lamps, xenon lamps, carbon arc lights, chemical lamps, low voltage mercury lamps, and high voltage mercury lamps are some of the light sources that may be used for ultra-violet ray irradiation. These lamps are available in regular stores, as H lamps, D lamps, V lamps and others made by Fusion System Co. for example.
In the ink jet printing method of the present invention, water-base solvent in the ink attachment is preferably vaporized by adding heat either before or concurrently with light irradiation. By so doing, a polymerization reaction is conducted efficiently and a harder ink film having a high chemical proof property is formed in a short period of time.
A method in which heating is accomplished by making a heat source contact the printing surface, or a method in which infrared light or microwave (magnetic wave with maximum wavelength at about 2,450 Mhz) is irradiated instead of making a heat source contact the printing surface, may be used as the heating method.
The present invention also covers printed materials which are printed with the ink jet printed method of the present invention.
Moreover, the present invention provides a printed substrate production method wherein printing is conducted on the printed substrate using, the ink jet printing method of the present invention with the water-base ink containing pigment including titanium dioxide as colorant.
Moreover, the present invention provides a printed substrate which is printed using the ink jet printing method of the present invention with the water-base ink containing pigment including titanium dioxide as the colorant.